In recent years, an inkjet printer, which discharges ink from its head onto a recording medium to record a desired image on the recording medium, is widely used. Examples of an ink for use in such an inkjet printer include wax inks which are solid at ambient temperature, solvent inks mainly containing an aqueous solvent or an organic solvent, and photo-curable inks which are cured by exposure to light.
Since such an inkjet printer discharges ink through discharge ports with a very small diameter provided in a head, there is a possibility that the ink adheres to the head, areas near the discharge ports, and other parts of the inkjet printer and the discharge ports become clogged with the dried and solidified ink. Therefore, various measures are taken to prevent clogging of discharge ports with ink.
Patent Document 1 discloses a technique for capping discharge ports while an inkjet printer does not perform image recording. However, if the printer is not used for a long period of time, the viscosity of ink near a recording head increases due to vaporization of a solvent so that clogging of the discharge ports is likely to occur. Further, clogging of the discharge ports with foreign matter such as dust in the air is also likely to occur. Such clogging of discharge ports becomes a cause of defective ink discharge.
Patent Documents 2 and 3 disclose a technique for wiping ink off areas near the discharge ports of an inkjet printer when the inkjet printer performs image recording or just before the end of image recording. However, the ink wiped off with a cleaning member adheres to the cleaning member by its surface tension, and therefore when wiped with such a cleaning member, the discharge-port surface is likely to get dirty. Further, there is also a problem that if the ink adhering to the cleaning member is solidified and then enters the discharge ports, the solidified ink causes defective ink discharge.
Patent Document 3 also discloses a technique for wiping ink off discharge ports using silicone oil or ethylene glycol as a cleaner. Patent Document 4 discloses a cleaner for removing an ink for electronic parts which contains a monomer component and a polyhydric alcohol or its derivative. Patent Document 5 discloses a cleaner containing glycol ethers as a main component, water, surfactants, and at least one other aqueous organic solvent as an additional components. Such a cleaner has a high ability to dissolve ink due to its additional component. However, if the additional component remains after cleaning, the remaining additional component slows down the evaporation of the cleaner or deteriorates the stability of ink supplied to a printer after cleaning.
Patent Document 6 discloses a cleaner for use in cleaning ink supply parts such as ink bottles and ink supply rollers and various printing plates such as screen printing plates and gravure printing plates which are used in printing processes of gravure printing, flexographic printing, offset printing, and the like.
However, those cleaners are intended to remove or peel off ink from substrates on which it has been printed or applied.
Under the circumstances, there has been a demand for a maintenance liquid for inkjet printers which offers excellent cleaning performance but does not soil an inkjet head member for inkjet ink, does not cause non-discharge of ink, and does not corrode inkjet printer components.    Patent Document 1: JP-A-59-111856    Patent Document 2: JP-A-8-1953    Patent Document 3: JP-B-62-9030    Patent Document 4: JP-A-2006-291191    Patent Document 5: JP-A-8-67839    Patent Document 6: JP-A-2005-120389